Switching of the topologically trivial and non-trivial quantum phase transitions in compressed 1T-TiTe2: Experiments and Theory

摘要

We report the structural, vibrational and electrical transport properties upto 16 GPa of the 1T-TiTe2, a prominent layered 2D system, which is predicted toshow a series of topologically trivial - nontrivial transitions underhydrostatic compression. We clearly show signatures of two iso-structuraltransition at 2 GPa and 4 GPa obtained from the minima in c/a ratio concomitantwith the phonon linewidth anomalies of Eg and A1g modes at around the samepressures, providing strong indication of unusual electron-phonon couplingassociated to these transitions. Resistivity presents nonlinear behavior oversimilar pressure ranges providing a strong indication of the electronic originof these pressure driven isostructural transitions. Our data thus provide clearevidences of topological changes at A and L point of the Brillouin zonepredicted to be present in the compressed 1T-TiTe2. Between 4 GPa and 8 GPa,the c/a ratio shows a plateau suggesting a transformation from an anisotropic2D layer to a quasi 3D crystal network. First principles calculations suggestthat the 2D to quasi 3D evolution without any structural phase transitions ismainly due to the increased interlayer Te-Te interactions (bridging) via thecharge density overlap. In addition to the pressure dependent isostructuralphase transitions, our data also evidences the occurrence of a first orderstructural phase transition from the trigonal (P-3m1) phase at higherpressures. We estimate the start of this structural phase transition to be 8GPa and the symmetric of the new high-pressure phase to be monoclinic (C2/m).